1. Field of the Invention
This invention generally relates to a liquid jetting device such as, for example, a humidifier for discharging water or vapor, a device for applying ink to an object and the like. More particularly, this invention relates to an ink jet printer for applying a jet of ink to a medium such as paper to be printed. Broadly, this invention is also concerned with a bubble detection circuit and method for use with such a liquid jetting device.
2. Description of the Related Art
FIG. 6 shows a conventional ink jet printer described in, for instance, Japanese Unexamined Patent Publication (Laid-Open) No. 6-336026.
In FIG. 6, reference numeral 1 designates a print head of the ink jet printer. This head 1 comprises a plurality of nozzles 2, a pressure chamber 17 formed in a housing 18, an ink path or passage 15, piezoelectric elements (or devices) 16a and 16b for changing the capacity or volume of the pressure chamber 17, and a heater 19 for heating the housing 18.
Further, an ink cartridge 6 provided with an ink container 4 is mounted on the housing 18. The ink container 4 communicates with the plurality of nozzles 2. Moreover, porous elements 9 and 13 for absorbing and holding ink are contained in the ink container 4. A heater 5 for heating ink is mounted on the outside surface of the ink container 4.
Next, an operation of this conventional ink jet printer will be described hereinbelow.
Usually, the ink passage 15 is filled with ink which is in a solid state. When a voltage is applied to the heater 5 mounted on the ink container 4 and to the heater 19 provided in the head 1, ink contained in the ink passage 15 and ink absorbed in the porous elements 9 and 13 are melted. Then, a voltage is applied to the piezoelectric elements 16a and 16b, which are in such a condition, to thereby vibrate these elements. Thus, the capacity of the pressure chamber 17 is changed, so that ink droplets are jetted out of the nozzles 2. As a result, the ink absorbed in the porous elements 9 and 13 are gradually supplied to the pressure chamber 17. Ink is jetted out of the head 1 by performing this operation, and is then caused to adhere to paper. Thus, printed matter is obtained.
The conventional ink jet printer has the following problem: when bubbles get into ink contained in the ink passage 15, ink cannot be normally discharged from the plurality of nozzles 2 so that printed matter obtained is thereby streaked, thus making it impossible to provide stable and high-quality printed matter.
Moreover, the conventional ink jet printer has no means for checking the presence or absence of a bubble before printing an image and so on. Thus, the conventional ink jet printer has a problem in that there is necessity for printing a test pattern to be used for determining whether or not ink is normally discharged.
Furthermore, in the case that normal printed matter is not obtained owing to the presence of bubbles when the test pattern is printed, the conventional ink jet printer should repeatedly perform the following process. Namely, in such a case, this printer first performs an ink supply recovery or resumption operation as a recovery measure. Then, this printer prints the test pattern again so as to check whether or not ink is normally discharged. Thus, this conventional ink jet printer has another problem in that it takes much time and costs to perform such a process.